design and construction of an audio surveillance · pdf file · 2017-04-24design...

Communications on Applied Electronics (CAE) – ISSN : 2394-4714

Foundation of Computer Science FCS, New York, USA

Volume 6– No.10, April 2017 – www.caeaccess.org

21

Design and Construction of an Audio Surveillance

System

I. A. Oguche Main Author

Elect. & Elect. Engineering College of Engineering

Univ. of Agric.,Makurdi, Nigeria

J. U. Agber Main Supervisor



N. S.Tarkaa Minor Supervisor



ABSTRACT Surveillance is the monitoring of the behavior, activities, or

other changing information, usually of people and events for

the purpose of influencing, managing, directing, or protecting

them. In this paper, an audio surveillance system was

designed, simulated and constructed by replacing discrete

components with an integrated circuit(CD2003) with the

view of taking advantage of electret microphone ability to

capture sound of low frequency and transmit it to the receiver

where the signal can be retrieved. The audio signal was then

amplified using two bipolar junction transistors (BJT),

modulated and transmitted via an antenna. A provision for

recording of the retrieved signal was made using a telephone

set for continual logs of information for retrieval purposes at

the receiver section. The circuit was designed and fully

implemented with a designed output power of 0.3watts which

transmitted within 8-12meters radius and waveforms from

proteus 8 professional and multism software were obtained

and compared for performance and evaluation. This short

range of coverage was designed and implemented with the

aim of avoiding major interference from the surrounding since

the system is meant to survey a small area like banking hall,

bulk cash rooms and other sensitive areas.

Keywords Electret, microphone, surveillance, antenna, waveform,

monitoring, retrieved

1. INTRODUCTION Surveillance is defined as covert observations of places and

persons for the purpose of obtaining information [1]. The term

covert infers that the operative conducting the surveillance is

discrete and secretive. Surveillance that maintains a

concealed, hidden, undetected nature clearly has the greatest

chance of success because the subject of the surveillance will

act or perform naturally. Remaining undetected during covert

surveillance work often involves physical fatigue, mental

stress, and very challenging situations. Currently, audio

signals are making their way to public surveillance. For

example, microphones are installed in locations with high

crime rate by street gangs [2]. The advantage of audio is that

the sensors are quite small and can be installed practically

anywhere. Their low power-consumption allows local power-

supply including wireless data transfer.

As population increases, the challenge in the rise in social

vices also increases. The increase in crime in the present time

has necessitated the need for security operatives, science and

technology to indulge in research works towards finding

solutions to combat this menace. In most cases, security

operatives lack concrete evidences for prosecuting a potential

criminal and this potential criminal go scot free. There are

times or situations where verbal evidences are provided in

court of law to evict or convict a suspect. In view of all this,

audio surveillance system is important and necessary.This

audio surveillance system employs the transmitting of audio

signal or information from some particular points to a single

receiver point. The principle of telecommunication, which the

audio surveillance system is based on, uses a transmitter that

generates or emits a particular radio wave frequency, which is

used as the carrier of this audio signal. The transmitter

electronically encapsulates the audio signal, magnifies and

transmits it at a particular frequency via an antenna. The

transmitted signal is received from the central reception point

within the coverage distance of the transmitter. The received

radio wave is then filtered, detected (demodulated) and

converted back to audio and is heard on the loud speaker.

The history of audio surveillance involves four major aspects,

the understanding of the science of sound, the evolution of

technologies to project sound over distance, the evolution of

devices to record sound, and laws to regulate the use of these

technologies. Much of the current legislation regarding

communications, recording, and wiretapping has its roots

deep in the 19th century. Humans have been recording events

for at least 2,000years, through images and later through text,

but the recording of sound is a surprisingly recent event [3].

2 LITERATURE REVIEW Surveillance has received a great attention in extreme active

application-oriented research areas in computer vision,

artificial intelligence, and image processing. Audio

surveillance is conducted over both wired and wireless

systems. The main focus in this paper is on wireless systems

because audio communications are converted into radio-wave

frequencies before transmission. The early use of monitoring

system was the tube camera that was deployed to broadcast

and monitor the industrial processing in the 1930s and 1940s

[4], [5]. The traditional video surveillance systems – normally

called Close-Circuit Television (CCTV) – was defective and

costly since they were deployed by security teams to observe

events in the scenes via visual display.

In recent decades, expansion in surveillance systems led to

expansion in various prominent domains of technology and

science such as homeland security, crime prevention through

indoor and outdoor monitoring, elder care, accident detection,

traffic monitoring, controlling and traffic flow analysis,




22

airborne traffic management, maritime traffic control,

counting moving object - pedestrians, vehicles, human

behavior understanding, motion detection, activity analysis,

identification, tracking and classification of vehicles, peoples,

and any object of interest [5] - [21]. Encryption and acoustic

surveillance are closely related, since encryption is one of the

principal ways in which the privacy of communications is

safeguarded. For this reason, acoustic surveillance, computer

encryption, and cryptology share a common history in many

respects [22].

In this paper the receiver section of the circuit has an RF

amplifier which is a simple common emitter amplifier using a

BF199, this is followed by the product detector using three

times BF199 transistors. The audio from the product detector

is passed through a simple low pass filter to the audio

preamplifier using a BC549C transistor, then on to the audio

amplifier using an LM386.

Work on an input amplifier for a FM-radio receiver with RF

selection (88-108 MHz) has been designed in the radio

section[25]. It has about 25 dB gains in the frequency range

88-108 MHz. Mirror frequency rejection is between 5 dB to 9

dB. Noise figure is about 7-10 dB at resonant frequency. The

amplifier works fairly well, when it is connected to the rest of

circuits to receive FM broadcast signals. The limitation of this

is work is the inability to effectively control noise range due

to high attenuation rate.A work on designing a short range

wireless USB-FM transmitter which can transmit data

contained in the USB flash drive over short distance using

ROHM® BU9458kv Semiconductor chip was done [26]. The

project has actually been done in two parts, designing and

analyzing. The first section is FM Transmission and the

second is USB-mp3 module. The FM Transmitter is designed

by using two BC-547 transistors. The USB mp3- Module is

designed using ROHM® BU9458kv Semiconductor chip. The

mp3 songs can be played directly from the USB flash drive by

using MODE-1(default mode) of the semiconductor chip

without programming it. Successful Transmission of audio

signal through the designed FM Transmitter is a proof of the

correctness of the design. The experimental results on FM

transmitter ensurethat the design is capable of transmitting

USB data if it is implemented completely on commercial

basis. The limitation of this system is the inability to transmit

on a longer distance and much distortion on the transmitted

data.

A walkie-talkie is a hand-held portable, bi-directional radio

transceiver. Major characteristics include a half-duplex

channel (only one radio transmits at a time, though any

number can listen) and a push-to-talk switch that starts

transmission. Hand-held transceivers became valuable

communication tools for police, emergency services, and

industrial and commercial users, and are also popular with

some amateur radio operators.The personal walkie-talkie has

now become popular again with the new U.S. Family Radio

Service and similar unlicensed services in other countries.

While FRS walkie-talkies are also sometimes used as toys

because mass-production makes them low cost, they have

proper super heterodyne receivers and are a useful

communication tool for both business and personal use.

Although this system works effectively, but it cannot record

transmitted information directly due to the way it is designed

[23], [24].

This research work of design and construction of audio

surveillance system is based on the principles of a walkie-

talkie which comprises a transmitter section and a receiver

section. Here, a recording device to cater for the recording of

the received FM signal. Hence, the recorded information can

then be retrieved for analysis and as evidence which is the

main core aim of this paper (audio surveillance system). The

transmitter section comprises the collection of audio sound,

magnifying it and transmitting it at a design frequency of

between 88-107MHZ via antenna, while the receiver section

comprises the frequency selectors, filtering devices and

decoding/detection of the collected audio signal before

recording and outputting the signal via speaker. In this paper,

Bipolar Junction Transistors (BJTs) are used in the design of

both the transmitter and receiver circuits but an integrated

circuit (IC) is used in the receiver sections to replace the

assemblage of several discrete components which helped

significantly to reduce loss of signals, noise, high attenuation

rate and economically elimination of cost of replacing

damaged components due to assemblage and testing.The

chosen frequency is 100MHz and the transmitter power is

0.3Watts to transmit at a distance of about 8-12m radius to

avoid major interference with other nearby systems and the

mixer type used here is double-balanced mixer(DBM) for a

fairly good output

3. METHODOLOGY Fig 1 shows the block diagram of the transmitter section. It

comprises the input block, which is basically a microphone, an

amplifier block and a converter/modulator block, to which an

antenna is attached. From the input , the signal is fed into the

amplifier section but before amplification, at TP1 from the

diagram, the signal from the microphone was tested, measured

and record for comparative analysis and the same method was

deplored at respectively to measure the amount of

amplification that had taken place before conversion,

modulation of the signal and transmission via the antenna.

Fig. 1: The block diagram of the transmitter

Fig. 2 shows the FM transmitter circuit diagram. It is made up

of the following main components: Oscillators, Microphones,

Modulators and Amplifiers among other discrete components.

It is the circuitry representation of the block diagram above

showing the two stages of amplification before feeding it into

the LC tank and then transmission via the antenna

TP3 TP2 TP1

Antenna

Input Amplifier Converter/Modulator




23

.

L1

C5

R7R6

R5

C3

C2

Q2

R3R2

R1

C1

Q1

R4 C4

Fig. 2: Transmitter Circuit Diagram

𝑉𝐵 =𝑉𝑐𝑐𝑅2

𝑅1+𝑅2 (1)

𝑅𝐵 = 𝑅1||𝑅2

Taking Base-emitter loop, KVL yields

𝑉𝐵 = 𝐼𝐵𝑅𝐵 + 𝑉𝐵𝐸 + 𝐼𝐸𝑅3 (2)

=𝐼𝑐

𝛽𝑓𝑅𝐵 + 𝑉𝐵𝐸 +

𝛽𝑓+1

𝛽𝑓 𝑅3

𝐼𝑐

𝛽𝑓 𝑅𝐵 + 𝛽𝑓 + 1 𝑅3 + 𝑉𝐵𝐸 (3)

Note that every parameter in eqn. 3 is already

known except RB which can be calculated. Eqn. (1) and (2) are

solved simultaneously to obtain R1and R2

Assuming derived operation points:

1. selecting 𝑅3 to make the voltage drop / 𝐼𝐸 𝑅3/ about

1volts for stability

2. 𝑅3about 10𝑅3. for transistors with 𝛽𝑓≈ 100, this

choice suppresses 𝛽𝑓variation by a fraction of about

10 compared to a design with 𝑅3 equal to zero. But

still allows 𝑅𝐵to be large enough to prevent

excessive shorting of the input signal to ground.

𝑉𝐵 = 𝑉𝐶𝐶 𝑅2

𝑅1+ 𝑅2 and 𝑅𝐵 =

𝑅1 𝑅2

𝑅1+ 𝑅2 (4)

We can deduce that:

𝑅1 = 𝑉𝐶𝐶 𝑅𝐵

𝑉𝐵𝐵 and 𝑅2 =

𝑉𝐶𝐶 𝑅𝐵

𝑉𝐶𝐶− 𝑉𝐵𝐵 =

𝑅1 𝑉𝐵𝐵

𝑉𝐶𝐶− 𝑉𝐵𝐵

𝑉𝐶𝐶 =9V, 𝑉𝐶𝐸= 4.5, 𝐼𝐶 = 1mA and 𝑉𝐵𝐸= 0.7

∴𝑅3 = 𝑉

𝐼𝐶 =

1

1 = 1Kohms

𝑅𝐵 = 10𝑅𝐸 = 10KΩ

∴ 𝑉𝐵𝐵 = 1

100 (10K + 101* 1K)+ 0.7

=1.8V

𝑅1 = 9∗10

1.8= 50ohms

𝑅1 =9∗10

9−1.8 = 12.5ohms

Taking loop along the collector,

𝑉𝑐𝑐 = 𝐼𝑐𝑅𝑐 + 𝑉𝐶𝐸+ 𝐼𝐸𝑅3

𝑅𝐶 =𝑉𝐶𝐶 − 𝑉𝐶𝐸−𝐼𝐸𝑅3

𝐼𝐶

= 9-0.3-1=9−4.5−1

1

=3.5KΩ

3.1 Design of FM Receiver Circuit Fig. 3 represents the receiver circuit diagram for effective

operation of the audio surveillance system after calculating

the corresponding values of the designed components

.




24

Fig. 3: Schematic diagram of FM 100MHz receiver

4. SIMULATION RESULTS OF

TRANSMITTER CIRCUIT USING

PROTEUS IDE Figure 2 represents the circuit diagram of the transmitter to be

simulated. Figure 4.1 shows the simulated output of the circuit

using wave sound. Figure 4.2 shows the simulated output of

the circuit using sinusoidal wave while figure 4.3 shows the

simulated output of the Colpitt’s Oscilator circuit.

Fig. 4.1: Simulation of designed Transmitter using WAV

sound

Fig. 4.2: Simulation of designed Transmitter using

sinusoidal wave

Fig. 4.3: Colpitt’s oscillator waveform

4.1. Results from Circuit Testing This section shows the results of the tests carried out on the

transmitter and the receiver circuits using Digital Oscilloscope

to view the various responses of the signal after being

transmitted and fed into the receiver and their corresponding displays are as shown in figures 4.3 – 4.10 respectively.

Figure 4.4: The waveform of the input signal to the base of

the first transistor of the transmitter circuit when fed with

audio signal.

R2

R6

C4

Q2

VC1

L1

C1

C2

C31nF

D1 TR1

TRAN-2P3S

C9

C11

TR2

TRAN-2P3S

C14

R9 C12

R5

Q1

C6

L3

R3

R4

C5C7

C8

L4

R7

R8

C10 C13

BAT

9V

SW1

1

1

R1

C16

C17

TR3

TRAN-2P3S

C18

D2

D3

R10

R11

R12

C19 C20 C21

C22

VD

AF

L2

L5




25

Figure 4.5: The waveform of the input signal to the base of

the second transistor of the transmitter circuit when fed

with audio signal

Figure 4.6: The waveform of the output signal to the LC

tank terminal of the transmitter circuit when fed with

audio signal.

Figure 4.7: Output of the receiver circuit (at speaker

terminal

Figure 4.8: Transmitted signal(oscillator output)

Figure 4.9: Received signal (at TP1 of RADIO)

5. CONSTRUCTION In constructing the circuit, the following steps were taken:

1. It was ensured that the components were assembled

externally to confirm the functionality of the various

components together before transferring them on the

vero board

2. It was equally ensured that every confirmed

damaged or faulty components were replaced.

3. It was also ensured that all flaws on the vero board

were removed to avoid bridging before powering

testing the circuit

The constructed circuit was packaged. Packaging helps to

provide:

i. Physical protection for the often sensitive

components like ICs which are vulnerable

to static charges.

ii. It enhances the beauty of the project.

iii. It reduces electrical shocks that may arise

from contact with parts of the circuit that

may have live voltages.

In this packaging, plastic is used for the encasement of this

project due to its insulation property. Weight, compatibility

and efficiency of the components are some of the factors

considered in the construction of this project. The finished

product of the transmitter is shown in Plate 3.1 and the

receiver shown in Plate 3.2. The combination of the two,

which forms the entire system is shown in Plate 3.3.

Plate 3.1: Receiver component of the audio surveillance

system.




26

plate 3.2: Transmitter component of the audio

surveillance system.

plate 3.3: Complete units of the system consisting of the

Transmitter and the Receiver.

6. DISCUSSION PROTEUS IDE was used to simulate the transmitter and

notable result was recorded as shown in Fig 4 and 5. Also the

same software was used on the Colpitt’s oscillator that

generated the result depict Fig 7. in a similar vein, after the

construction, Fig. 8 shows the waveform of the input signal to

the base of the base of the first transistor of the transmitter

circuit when fed with audio signal and Fig. 9: The waveform

of the input signal to the base of the second transistor of the

transmitter circuit when fed with audio signal. The waveform

of the output signal to the LC tank terminal of the transmitter

circuit when fed with audio signal was depicted in Fig. 10

with Output of the receiver circuit (at speaker terminal) shown

in Fig. 11 and Transmitted signal (oscillator output) in Fig.

12, Received signal in Fig. 13. The Fig. 3 depicts the AM/FM

radio monolithic integrated circuit which is widely used for

AM/FM receivers with features such as AM HF amplifier,

local oscillator, mixer, IF amplifier, detector circuit, FM HF

amplifier, local oscillator, mixer, IF amplifier, discriminator

circuit, AGC circuit and the AM/FM band selection circuit

was used to achieve the possible result. Fig. 14 shows

waveform of the output signal from speaker terminal of the

transmitter circuit when fed with audio signal has your

transmitter circuit speaker terminals. The Fig. 15 through 17

shown the Receiver component of the audio surveillance,

Transmitter component of the audio surveillance system and

complete units of the system consisting of the Transmitter and

the Receiver respectively.

6.1 Conclusion In this research, an audio-based surveillance system was

designed and implemented using CD2003 in place of discrete

components. The performance of the system was

significantly improved by replacing the discrete components

with the\integrated circuit in the design approach. The

correlation muting system and the FLL (Frequency- Locked-

Loop) make it easy to tune and higher performance portables

and clock radios, variable-capacitance, diode tuning and

station presetting facilities were recorded.

7. ACKNOWLEDGEMENT Our thanks to the experts who have contributed towards the

development of the template.

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